1. Field of the Invention
The present invention relates to a copper-based metal polishing solution and a method for manufacturing a semiconductor device.
2. Description of the Related Art
A polishing solution for a Cu film or a Cu-alloy film, which consists of a slurry of amine-based colloidal silica or a slurry added with K.sub.3 Fe(CN).sub.6, K.sub.4 (CN).sub.6, or Co(NO.sub.3).sub.2, is disclosed in J. Electrochem. Soc., Vol. 138, No. 11, 3460 (1991), VMIC Conference, ISMIC-101/92/0156 (1992) or VMIC Conference, ISMIC-102/93/0205 (1993).
Unfortunately, the above polishing solution has the following problem since there is no difference between the Cu film dissolution velocity of the polishing solution during dipping and that during polishing.
In the formation of an interconnecting layer as one manufacturing step of semiconductor devices, an etch-back technique is employed in order to remove steps from the device surface. This etch-back technique is a method in which a trench is formed in an insulating film on a semiconductor substrate, and a Cu film is deposited on the insulating film including the trench and polished by using a polishing solution, thereby forming a buried interconnecting layer by leaving the Cu film behind only in the trench. After this etch-back step, the Cu interconnecting layer remaining in the trench is brought into contact with a polishing solution. Therefore, if a polishing solution of the composition discussed above by which no difference is obtained between the Cu film etching rate during dipping and that during polishing, the Cu interconnecting layer is further etched by the polishing solution. As a result, the surface of the Cu interconnecting layer becomes lower than the surface of the insulating film. This makes it difficult to form an interconnecting layer whose surface is level with the surface of the insulating film, resulting in a low flatness. In addition, the resistance of a buried Cu interconnecting layer formed in this manner becomes higher than that of a Cu interconnecting layer which is so buried that its surface is level with the surface of an insulating film.